Chevrolet Q&A

94 Chevy Suburban 350 5.7 4 wheel drive..
My husband put in a CD player in the truck in February. Under the ash tray there is a box with plugs into it. He re plugged everything back into the box and put the dash back together. He found a plug hanging that didnt get put back. Since them my truck is getting 9 MPG. A transmission guy today Diagnosed it but my husband keeps telling me that this plug hanging could not be the cause of the miscommunication between the PMC and 2-3rd Solenoid. All the problems I am having with 1st, 2nd and 4th gears not shifting and only being able to drive in 3rd started right after the CD player was put into the truck. Can a plug under the dash not being plugged in cause communication problems between the PCM and 2-3rd Solenoid in the transmission?
Thank you so much for your help with this..
Staci